[Engine-devel] Floating Disks implementation in REST-API

[Itamar Heim]

On 04/17/2012 05:26 PM, Ori Liel wrote:
>>
>>>> Floating disks should be both in the root context, and also in the VM
>>>> context for each VM the floating disk is attached to, right? So floating
>>>> disks would appear 1+N_attach times in the API, once in the root
>>>> context, and once for each VM they are attached to.
>>>>
>>>
>>> IIUC a floating disk is not associated with the VM in any way, and should
>>> not appear in that VM's collection of disks. There's a similar feature of
>>> activate/deactivate disk (http://www.ovirt.org/wiki/Features/HotPlug).
>>> A deactivated disk is still associated with the VM, and should appear in
>>> the VM's collection of disks. Perhaps this is the source of confusion.
>>
>> No that isn't it. I think have a bit of terminology mismatch. According to:
>>
>> http://www.ovirt.org/wiki/Features/DetailedFloatingDisk
>>
>> i think your use of the word floating is correct. I got confused as i
>> thought that any disk could be floating, whether it was attached to 0
>> VMs, 1 VM, or 2 or more VMs.
>>
>> So before we go further, let's get things straight:
>>
>>   - disk without any VMs =>  floating. It appears in the root context.
>>   - disk attached to 1 VM =>  normal state. It appears in the VM context.
>
> I think this type of disk should be shown in both contexts.
>
> If a user is looking at http://{host:port}/disks, I think he intuitively
> expects to see all disks (attached or unattached). A disk will contain
> reference to the VMs which it is attached to, and thus:
>
> - No VM-ids          -->     floating disk.
> - One VM-id          -->     regular disk.
> - Multiple VM-ids    -->     shared disk.

iirc, shared disk is a flag on the disk to allow it to be shared. 
doesn't mean it is shared yet, rather can be shared.

>
>>   - disk attached to 2 VMs =>  shared disk. It appears in both VM contexts.
>>
>> Is that correct?
>>
>> Also can someone explain on how floating and shared disks are actually
>> implemented in the BE? I imagine it's one of two ways:
>>
>>   =>  The BE keep a global list of disks, each disk with zero or more
>> references to a VM.
>>   =>  The BE keeps a special "floating" state independent of the number
>> of VMs that it is attached to.
>>
>> Thanks,
>> Geert
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